This invention relates to accessing information, such as lot code numbers, from workpieces as they move down a manufacturing line.
In the fabrication of many types of workpieces, it is important to keep track of lots during the manufacturing process, especially when many different types of a general product are manufactured in the same plant. This is typically true, for example, in the fabrication of printed circuit boards having various circuit configurations. In order to ensure that each product receives the appropriate processing, code numbers are assigned to each lot according to the required fabrication sequence for that lot. Identification of these code numbers as the lots travel through the plant not only ensures appropriate processing, but also facilitates inventory control and helps control production schedules.
At the present time, the lot codes typically appear on documentation which accompanies the boards to various plant locations. Such documentation can be easily lost or erroneously switched with other lots. It is, therefore, desirable to include the lot code numbers on the boards themselves. It has been suggested, for example, that chemically resistant markers could be placed on printed circuit boards (see, for example, U.S. Pat. No. 4,584,238). However, it is difficult to provide any single material which will be resistant to all the caustic chemicals and severe processing involved in circuit board fabrication.
It is, therefore, an object of the invention to provide information which is an integral part of the workpieces and a means of accessing that information as the workpieces move down a production line.